JPH05115904A - Method for rolling seamless steel tube - Google Patents

Abstract

PURPOSE:To prevent bend in the rolling tip part of a seamless tube by starting rolling after the tip part of a tube stock which is bored with a boring machine is cooled. CONSTITUTION:When the rolling tip part of the seamless steel tube 2 is transported under a cooling water header 3, the seamless steel tube 2 is stopped and turning rollers 4 are lifted. After the seamless steel tube 2 is supported in the state that the tube is separated from carrier rollers 1 with the turning rollers 4, the seamless steel tube 2 is revolved around the axial line by revolving the turning rollers 4. Simultaneously cooling water is injected from the cooling water header 3 and the seamless steel tube 2 is cooled. In this way the deformation resistance in the cooled rolling tip part is increased and the part isn't downward bent even in the state that the tip part after rolling isn't supported with the rollers 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling a seamless steel pipe which prevents bending of the rolling tip.

[0002]

2. Description of the Related Art When a seamless steel pipe is manufactured by a mandrel mill, it is carried out by the process shown in the process chart of FIG. That is, the round billet 21 is heated in the rotary hearth heating furnace 22 to a temperature suitable for rolling. Next, the heated round steel piece 21 has a hole penetrating in the longitudinal direction at the center thereof by a punching machine 23 to form a raw tube 24. Then, the mandrel bar 25 is rolled by the elongator 26, the mandrel bar 25 is inserted into the hollow portion of the raw pipe 24, and the raw pipe 24 in this state is rolled by the mandrel mill 27 having a plurality of rolling rolls. The shell of the raw pipe 24 is stretched by the rolling roll 26 and the pipe of the mandrel bar 25, and is formed into a seamless steel pipe having a wall thickness close to a predetermined thickness. Furthermore, it is molded to the final size with the sizer 30,
It is cooled in the cooling floor 31.

In the rolling by the mandrel mill, for example, as disclosed in Japanese Patent Laid-Open No. 61-154704, the temperature of the raw tube is prevented from lowering, and the cross-sectional shape is controlled by making the temperature uniform in the longitudinal direction. The emphasis has been placed.

[0004]

In the rolling of the seamless steel pipe by the mandrel mill as described above, the seamless steel pipe at the intermediate stage during rolling by the mandrel mill 27 has a high rolling temperature of 1100 ° C. or higher, and the following sizer Even at the exit of 900, the temperature is considerably high at 900 to 1000 ° C. Since the deformation resistance at this temperature is as small as around 10 kg / mm ^{2 in} the case of 0.2 to 0.45% carbon steel, for example, as shown in FIG. 7, the rolling tip has one roll 30 to the next roll 3
Until it reaches 1, there is nothing to support from below,
There was a problem of turning downward due to its own weight.

An object of the present invention is to solve the above problems of the prior art and to provide a method for rolling a seamless steel pipe in which the rolling tip of the seamless pipe is not bent.

[0006]

In the method for rolling a seamless steel pipe according to the present invention, the rolling is started after cooling the tip portion of the raw pipe pierced by a piercing machine.

Further, the invention as an embodiment of the invention described above is such that a range of a length corresponding to a rolling material outlet roll interval at least after completion of final rolling from a rolling tip portion of a rolled material is cooled at 50 to 200 ° C. in a temperature range. To do.

[0008]

In the method for rolling a seamless steel pipe according to the present invention, the rolling is started after the tip portion of the raw pipe pierced by the piercing machine is cooled. As a result, the deformation resistance of the rolling tip portion which has become low in temperature is increased, and even if the rolled tip portion is not supported by the roll, it does not bend downward.

Further, the invention as an embodiment of the above-mentioned invention is such that a range of a length corresponding to an interval between rolled material outlet rolls after completion of final rolling from a rolling tip portion of a rolled material is cooled at 50 to 200 ° C. in a temperature range. To do. As a result, the deformation resistance can be increased to the extent that bending does not substantially occur.

[0010]

EXAMPLE A method of rolling a seamless steel pipe according to one example of the present invention will be described with reference to FIG. A cooling water header 3 with a nozzle for cooling the seamless steel pipe 2 is provided on the transport roller 1 before entering the mandrel mill. Then, a plurality of vertically movable turning rollers 4 for rotating the seamless steel pipe 2 around the axis are provided. When the rolling front end 2a of the seamless steel pipe 2 is conveyed to below the cooling water header 3, the seamless steel pipe 2 is stopped and the turning roller 4 is raised. Then, after supporting the seamless steel pipe 2 with the turning roller 4 in a state of being separated from the transport roller 1, the turning roller 4 is rotated to rotate the seamless steel pipe 2 around the axis. At the same time, cooling water is sprayed from the cooling water header 3 to cool the seamless steel pipe 2. The cooling length (L) of the seamless steel pipe 2 may be set larger than the distance between the adjacent rolling rolls of the sizer.

FIG. 2 is a graph showing the relationship between the rolling temperature and the deformation resistance of a seamless steel pipe when a strain of 0.2 is applied at a strain rate of 0.3% / sec. The curve plotted with ◯ is 1C
r-0.5% Mo steel, the curve plotted with x is 0.4
5% C steel, the curve plotted with Δ is for 0.2% C steel. As is clear from the figure, when the rolling temperature rises, the deformation resistance decreases. A similar tendency is observed in the bending deformation of the pipe due to its own weight, and the bending deformation due to its own weight becomes remarkable as the temperature becomes higher when the pipe is horizontally supported by a cantilever.

The bending deformation of the pipe occurs after leaving the sizer, which is the final rolling step. Therefore, the bending deformation of the pipe can be solved by cooling the temperature of the end portion of the pipe that becomes the cantilever so that the deformation does not occur before the pipe leaves the sizer.

The cooling step can be inserted after the piercer of FIG. 6 shown previously. Of course, the cooling may be performed twice or more. The cooling target temperature is basically determined by the material and size of the tube. However, in the case of rolling with a mandrel mill, the size of the tube is limited to a certain range, and in order to prevent bending, in the case of carbon steel, 900 ° C or less at the sizer outlet is a standard. In addition, Cr-
In the case of Mo steel, this upper limit temperature rises by about 100 ° C.
The sizer rolling temperature is 900 to 1000 ° C.
The purpose is achieved by lowering the temperature by 00 ° C. This 100
It is also possible to perform cooling at ℃ at the upstream side of the process. For example, when the cooling is performed at the inlet of the elongator, the elongator rolling temperature is about 1150 ° C. sell.

The cooling range of the tube must be equal to or larger than the roll interval at the sizer outlet. When cooling is performed at the inlet of the mandrel mill, the cooling range may be determined in consideration of stretching by the mandrel mill and sizer. For example, when the roll interval at the sizer outlet is 1 m and the mandrel mill and sizer are used to stretch the film three times, a range of about 350 mm from the tip may be cooled.

Cooling is performed by water cooling. Of course, other refrigerants may be used, but generally the cooling capacity is inferior to that of the case of using water.

[0016] Since excessive supercooling hinders rolling, it is necessary to set the lower limit of the cooling temperature based on the size and material of the seamless steel pipe to be rolled, but most of them are The purpose can be sufficiently achieved by the control method of lowering the temperature by 50 to 200 ° C. as compared with the uncooled portion. In addition, it is not preferable for rolling to set the cooling range to be larger than necessary.

FIG. 3 shows a distribution chart of the bending amount of the tip portion of the seamless steel pipe rolled by the method of the present invention, and FIG. 4 shows a distribution chart of the bending amount of the tip portion of the seamless steel pipe rolled by the conventional method. .. Further, Table 1 shows the results of the cooling conditions and the bending amount of each steel type.

[0018]

[Table 1]

The seamless steel pipe used for measuring the bending amount is
Finished dimensions are outer diameter 172mm, wall thickness 41mm, length 12m.
As shown in FIG. 5, the bending amount of the dial gauges 5a and 5b are arranged at positions 30 mm and 500 mm from the end of the seamless pipe 2 so that the tips of the contact points are on the same horizontal plane. It was the difference. As described above, an example of the measured value is shown in FIG. 3 and a comparative example is shown in FIG. 4, but clearly in FIG. 3, the distribution of the bending amount is biased toward the smaller side, and the effect of the present invention appears. I understand that
The same results as in Table 1 and FIG. 3 were obtained for other seamless steel pipes having different dimensions.

[0020]

According to the present invention, the bending of the seamless steel pipe can be prevented.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a method for rolling a seamless steel pipe according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between rolling temperature and deformation resistance.

FIG. 3 is a distribution diagram of the bending amount of the tip of a seamless steel pipe rolled by the method for rolling a seamless steel pipe according to one embodiment of the present invention.

FIG. 4 is a distribution diagram of the bending amount of the tip of a seamless steel pipe rolled by a conventional method for rolling a seamless steel pipe.

FIG. 5 is an explanatory diagram showing a method for measuring a bending amount of a tip of a seamless steel pipe.

FIG. 6 is a manufacturing process drawing of a seamless steel pipe.

FIG. 7 is an explanatory view showing a bent state of a seamless steel pipe tip.

[Explanation of symbols]

 1 Conveyor roller 2 Seamless steel pipe 3 Cooling water header 4 Turning roller 5a Dial gauge 5b Dial gauge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshio Suzuki, Marunouchi 1-2-2, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Hidenori Yasuoka 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Inside the steel pipe company

Claims (2)

[Claims] 1. A method for rolling a seamless steel pipe, which comprises cooling the tip portion of a raw pipe pierced by a piercing machine and then starting rolling. 2. A range of a length corresponding to a rolling material outlet roll interval after at least the final rolling from the rolling front end portion of the rolled material is cooled by 50 to 200 ° C. in a temperature range. A method for rolling a seamless steel pipe as described.